Electronic circuits often operate on or process both analog and digital signals, sometimes called mixed-signal. Some sensors or transducers as well as natural properties or attributes, such as temperature, pressure, and the like, either constitute analog quantities or, in the case of sensors, often produce analog signals. Also, some transducers accept as inputs analog signals. Conversely, signal-processing circuits and building blocks increasingly use digital signals and digital techniques for reasons such as repeatability, stability, flexibility, and the like, as person of ordinary skill in the art understand. To interface the signal-processing circuits with analog circuits, signal conversion circuits are used. In addition, standalone analog circuitry are often used in electronic circuits, such as integrated circuits (ICs).
Because of the above developments and trends, a variety of analog circuitry (either alone or in a mixed-signal context) are used to perform a number of tasks, such as amplification, comparison, signal conversion, and the like. Analog circuitry often uses one or more types of signal sources, such as voltage sources or current sources. In the case of ICs, the current signals are usually generated using circuitry integrated in the IC, sometimes also using one or more external signals provided to the IC. Calibration of current signals (e.g., bias currents) of relatively small values are usually performed by amplifying the current (even though doing so introduces errors), and measuring the amplified current.
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